The present invention relates to a turret with a housing to be connected to a machine tool, with a rotatably mounted toolholder to receive machining tools, and with an electric drive to swing the toolholder into a particular operating position for the machining tools. The electric drive has a rotor and a stator with coil windings. The rotor of the electric drive is connected to the toolholder and the stator with elements of the housing. The rotary movement for the toolholder is generated without gearing and is performed directly by the electric drive. The rotor enclosing the stator.
DE 199 19 553 C2 discloses a generic, gearless turret having a rotatably mounted toolholder with at least two tools which may be swung or rotated into a particular working position for a tool by an electric pivoting drive. The toolholder is connected non-rotatably to a hollow shaft, and, by way of this hollow shaft, is rotatably mounted in the housing of the toolholder. A so-called ring motor is used as the pivoting drive, so that the electric motor, free of additional converting mechanical power transmission elements, engages the hollow shaft directly and by it generates pivoting movement for the toolholder.
The ring motors used for this purpose in the state of the art are electric motors with an electric winding in the stator, so that torque may be applied to the hollow shaft, which shaft is rigidly connected to the toolholder so as not to rotate. The ring motor employed in the state of the art is in the form of an internal rotor, that is, the stator connected to the housing along with the coil elements encloses the rotor on the side of the external circumference. This rotor is connected to the toolholder as an integral part of the hollow shaft.
The conventional ring motor is in this instance mounted in the area of the free end of the hollow shaft. The toolholder is in contrast rigidly mounted together with its machining tools on the other free end of this shaft. The respective structure occupies much installation space, especially on the housing side, so that a xe2x80x9cslimxe2x80x9d housing cannot be built with the conventional solution. This conventional arrangement limits the installation potential for the conventional turret, especially if this turret is to be used for machine tools which cannot provide the installation space required precisely because of their size or configuration. Since, in addition, the electric drive for the toolholder with the machining tools is mounted a relatively great distance from this toolholder, the respective power introduced for drive power is not the optimum, due to the hollow shaft acting as a torsion spring.
DE 197 19 173 A1 also discloses a generic turret with switchgear having a conical braking surface and a frontal braking surface on first and second brake disks movable relative to each other. This particular frontal brake surface is spaced from the respective tapering braking surface at a distance such that during braking the tapering braking surface initially acts to center and decelerate the movement of one brake disk to stop and fix the state of rest (switching position) with high positional accuracy by the frontal brake surface. As a result, the conventional switching device for the turrethead is made up of a small number of simple elements which are robust and long-lasting. The switching device of high-torque and low-speed motor may be moved into a precise angular position. In the case of the conventional solution, the ring motor is again positioned on the housing side, as with the conventional solution described earlier, so that the conventional solution cannot be readily applied, especially under cramped installation conditions.
DE 37 01 090 A1 discloses a switchable-angle modular unit for machine tools, also especially for use with turretheads. The modular unit has a stationary element with a component mounted rotatably around it, a drive motor, gearing, a detent device, and a signal device for registering the angular positions of the rotatable element. The signal device includes a plurality of zero-current detection or coding elements introduced into one of the opposite rotatable elements and a decoding or reading device mounted in another element and operating in conjunction with it. This conventional configuration makes it possible to effect position-oriented recognition of the angular position of the rotatable element, without occurrence of false signals triggered by bounces and without the need for additional installation space. On the contrary, contact-free recognition of the indexing position is possible. The components of the switchable-angle component in question are mounted for the sake of space conservation on the tool disk or toolholder, specifically in the transitional area between the toolholder and the stationary housing elements of the turret. Because of the cramped installation space at the installation location in question, only an electric motor small in structure may be employed. Such motor has relatively low power. Transmission of drive torque to the toolholder or the tool disk by gearing also consumes drive output along with installation space. Because of the great number of parts, the conventional solution is costly in production and susceptible to the breakdowns which may occur.
Objects of the present invention are to provide improved turrets requiring only a small installation space on the machine tool side for fastening the turret in position, achieving higher output for the electric drive, and transmitting a higher drive output to the toolholder so that more or less torsion-proof machining can be accomplished with the tools.
The foregoing objects are obtained by both the rotor and the stator being enclosed by the toolholder, and the rotor resting directly against the toolholder to be rigidly connected to the toolholder for transmission of torque. The rotor-stator assembly forms an external rotor for the electric drive, one in which the rotor rotates externally with the toolholder. The stator is mounted inside the housing. Since the external rotor is integrated entirely into the toolholder itself, where more installation space is available, a drive design can be produced which is substantially stronger than that of the conventional solutions. In conventional solutions, the interior rotor must enclose a hollow shaft of smaller diameter, so that less winding space is available for the drive design. As a result of integration of the external rotor-motor into the toolholder, the drive output is transmitted directly to the toolholder without the use of transmission gearing. Since the drive design transferred to the interior of the toolholder requires no installation space on the housing side itself of the turret, a xe2x80x9cslimxe2x80x9d turret is produced on its housing side, and requires little installation space on a machine tool. Especially with smaller machine tools or with ones which have little installation space relative to the machining situation it is possible only with the turret design of the present invention to make successful use of electric drive concepts for swinging the tool disk.
In addition, the turret of the present invention has no drivable hollow shaft. Thus, the high number of elements is reduced, lowering production costs and reducing the possibility of wear which results in increased down time for the turret. It has been found to be especially advantageous to design the electric drive as a synchronous motor. Since the speed of such motors depends on the frequency, but is independent of the load applied, speed-stable control is possible for the tool disk or the toolholder, regardless of the number of machine tools mounted on the holder and regardless of their weight or the respective machining situation. Since the turret claimed for the invention manages without transmission gearing, the drive concept as a whole is designed to be relatively rigid to favor machining accuracy. Although the overall drive concept is essentially an integral part of the tool disk, undesirable vibrations, which could have an undesirable effect on machining accuracy, do not occur.
In a preferred embodiment of the turret of the present invention, the outer circumference of the rotor is spaced a radial distance from the longitudinal axis of the turret, which distance is greater than half the respective distance of an outer circumferential section of the toolholder from this longitudinal axis. The stator is in this case mounted in the area of the free end of the columnar housing element, which extends stepwise in the direction of the toolholder up to a diameter which is larger than a base housing element over which the toolholder is mounted on the housing of the turret.
In view of these measures, use of an electric motor built with a large diameter with a large number of rotor and stator windings is possible. In this way, a high degree of power and torque can be achieved for the drive of the toolholder.
In an especially preferred embodiment of the turret of the present invention, a locking device is provided between toolholder and the housing. The locking device is preferably in the form of a brake, in particular a multiple-disk brake, or of a coupling, especially a serrated clutch (Hirth gearing, serration). The locking device makes it possible to fix the toolholder definitively in its machining position after being swung. The forces occurring in machining with the machine tools need not, as is the case with the conventional solution disclosed in DE 199 19 553 C2, be absorbed by the relatively low-power electric drive. Rather, the load is completely removed from the electric drive because of the locking device, and power is introduced into the housing exclusively by way of this locking device.
On the basis of the installation space available on the toolholder, the external rotor motor of the present invention can have substantially larger dimensions than the conventional internal rotor motor. Consequently, higher drive power is also available. Depending on the machining situation, the electric power of the external rotor motor may also be entirely sufficient for reliable absorption of the machining forces without a locking device.
In a preferred embodiment of the turret of the present invention, the locking device is operated hydraulically or pneumatically by way of an operating device. Very high braking or coupling forces can be made available by way of appropriate actuation. Forces of any intensity arising in operation can then be transferred into the housing of the turret without causing failure of this turret.
In another preferred embodiment of the turret of the present invention, the stator may be cooled by a cooling device, especially one involving water cooling. The cooling lines are mounted in a part of the carrier as part of the housing. Because of the corresponding cooling device, the heating that might occur in the stator at markedly higher torque values can be absorbed and transferred to the exterior so that heating of material, something which may occasionally impair zero-backlash and high-precision machining, cannot occur, either in the housing or in the toolholder.
In another preferred embodiment of the turret of the present invention, the holder element has a guide channel in which at least delivery of current for the electric drive takes place. The drive can be provided with current for the electric drive from the interior of the housing to conserve space. The holder element in the housing can also be configured such that shafts actuatable by a separate drive motor could be guided to the toolholder in such a way that actuatable machine tools on the toolholder could be used. A corresponding energy transmission and drive concept is disclosed in DE 40 18 543 C1 and EP 0 302 998 A1. This conventional solution could be transferred to the turret of the present invention.
In another preferred embodiment of the turret of the present invention, the respective position of the pivotable toolholder relative to the fixed housing can be detected by a sensor device, in particular an angular position transmitter. A reading head of the angular position transmitter is mounted preferably on the holder element. This head has as an additional element a measuring wheel which is mounted on the front side of the toolholder and pivotable with it. The corresponding monitoring device is also mounted inside the toolholder or tool disk to conserve space. In addition, the accompanying sensor or monitoring device makes it possible to actuate the electric drive by a suitable control concept in such a way that sure positioning of the machine tools for a forthcoming machining step is made certain.
Other objects, advantages and salient features of the present invention will become apparent from the following detailed description, which, taken in conjunction with the annexed drawings, discloses a preferred embodiment of the present invention.